Power tool attachment part

ABSTRACT

An attachment part for tightening joints includes: an elongate housing including an upper housing part and a lower housing part, an input gear wheel for connection to an output shaft of a power wrench, arranged at a first end of the housing, an output gear wheel for connection to a joint to be tightened, arranged at a second end of the housing, and at least one intermediate gear wheel arranged inside the housing to transmit rotation of the input gear wheel to the output gear wheel, wherein each gear wheel has outer slanted teeth that connect the gear wheels and transmit said rotation there between.

TECHNICAL FIELD

The invention relates to an attachment part for providing a torque froma torque wrench to a joint.

A power wrench attachment part is generally used in confined spaceswhere it is not possible to use an ordinary power wrench, due to that itis difficult to access the bolt or nut of the joint to be screwed. Anattachment part is also known as a crowfoot, a front part attachment oran offset attachment. Below it will be referred to as an attachmentpart.

BACKGROUND

An attachment part includes a number of gear wheels that transmit arotating movement from an input gear wheel to an output gear wheel. Thegear wheels are generally located in a straight row, teeth againstteeth, inside an elongate housing. In addition to the thickness of thehousing wall the length of the attachment part corresponds to the sum ofthe width of the gear wheels. The width of the attachment partcorresponds to the housing wall and the width of one gear wheel, and theheight of the attachment part corresponds to the housing wall and theheight of one gear wheel plus the height of the bearing arrangement,which is conventionally located between the gear wheels and the housing.

As is indicated above an attachment part is generally used in confinedspaces. Therefore, the size of it is an important feature. Further, theefficiency and accuracy of the attachment part is dependent on theheight of the gear wheels, i.e. the length of the teeth engagement. Theuse of gear wheels with slanted teeth increases the length of the teethengagement, and hence both the efficiency and the accuracy of theattachment part. This implies that an attachment part with slanted teethmay be utilised at higher torques, and at the same time provide a morereliable torque. On the other hand, the use of gear wheels with slantedteeth will give rise to axial forces, which will act to tilt the gearwheels and create tensions in the attachment part.

Therefore, slanted gear wheels are supported in a manner that restrictstheir ability to tilt. Conventionally slanted gear wheels are arrangedon a central shaft that is supported by both radial bearings and axialbearings. A disadvantage of this conventional arrangement is that thebearings build on the width of the attachment part. Further, the rigidarrangement of the gear wheels will give rise to tensions which may leadto fatigue and ruptures in the material.

Hence, there is a need of an attachment part that has both a highefficiency and a high accuracy.

SUMMARY OF THE INVENTION

An object of the invention is to provide an attachment part with acompact design and with a relatively high efficiency and accuracy.

This object is achieved by the invention according to claim 1, whichrelates to an attachment part for tightening joints, comprising:

-   -   an elongate housing including an upper housing part and an        interconnected lower housing part,    -   an input gear wheel for connection to an output shaft of a power        wrench, which input gear wheel is arranged at a first end of the        housing,    -   an output gear wheel for connection to a joint to be tightened,        which output gear wheel is arranged at a second end of the        housing, and    -   at least one intermediate gear wheel, which is arranged inside        the housing to transmit the rotation of the input gear wheel to        the output gear wheel, wherein each gear wheel has outer slanted        teeth that connect the gear wheels and transmit said rotation        there between.

Further, the at least one intermediate gear wheel comprises:

-   -   an upper race, which is arranged inside the at least one        intermediate gear wheel and faces the upper housing part,        wherein balls are arranged in said upper race at least partly        inside the at least one intermediate gear wheel to support an        upper part of it with respect to the housing, and    -   a lower race, which is arranged inside the at least one        intermediate gear wheel and faces the lower housing part,        wherein balls are arranged in said lower race at least partly        inside the at least one intermediate gear wheel to support a        lower part of it with respect to the housing.

In one specific embodiment of the invention the upper and lower racesare arranged at a position inside the at least one intermediate gearwheel that allows the whole of the balls to fit inside the at least oneintermediate gear wheel.

In another embodiment of the invention the balls in the upper and lowerraces are supported by the respective housing parts via upper and loweraxial supports, respectively, which include an flex portion that allowsthe at least one intermediate gear wheel to flex with respect to thehousing.

In yet another embodiment of the invention the upper and lower axialsupports include a body portion that is clamped into through holes inthe respective housing part, and a circular flange that is arranged tosupport said balls, and wherein said circular flange is separated fromthe body portion via a flex portion, which allows the circular flange toflex with respect to the housing.

The upper and lower axial supports may include an abutment portionarranged to abut the housing.

In another embodiment the balls in the upper and lower races are fullysupported by upper and lower axial supports, respectively, which axialsupports are connected to each other via an attachment piece that runsthrough the centre of the intermediate gear wheel, such that an upperand lower axial support, balls, and a gear wheel forms a releasable gearpackage.

The attachment piece may be a screw wherein one of the axial supportshas a threaded opening inside which the tip of the screw is to bescrewed.

The upper and lower axial supports may include a body portion that isarranged to be received in through holes in the upper and lower housingpart, respectively.

In one specific embodiment of the invention the output gear wheel isjournalled inside the housing, by means of balls that are arrangedbetween the upper and lower outer periphery of the output gear wheel andthe respective housing part.

In another embodiment of the invention the attachment part includes atleast two intermediate gear wheels, or even three intermediate gearwheels.

In yet another embodiment of the invention the housing parts are heldtogether by screws, and wherein there is a gap between the screws andone of the housing parts, such that there is an allowance inside whichthe housing parts may slide with respect to each other.

Other features and advantages of the invention will be apparent from thefigures and from the detailed description of the shown embodiments.

SHORT DESCRIPTION OF THE DRAWINGS

In the following detailed description reference is made to theaccompanying drawings, of which:

FIG. 1 shows an attachment part according to a specific embodiment ofthe invention;

FIG. 2 shows the attachment part of FIG. 1 with the upper housing partremoved;

FIG. 3 shows a longitudinal section of an attachment part according to aspecific embodiment of the invention;

FIG. 4 shows a detailed view of a central portion of the attachment partshown in FIG. 3;

FIG. 5 shows a close up of the detailed view of the central portionshown in FIG. 4;

FIG. 6 shows a detailed view of an end portion of the attachment partshown in FIG. 3;

FIG. 7 shows a second embodiment of the attachment part according theinvention;

FIG. 8 shows the attachment part of FIG. 7 from the opposite direction;

FIG. 9 is a top view of an attachment part according to a thirdembodiment of the invention;

FIG. 10 is a view from below of an attachment part according to thethird embodiment of the invention;

FIG. 11 is a sectional view of the attachment part according to thethird embodiment; and

FIG. 12 is a perspective cut view of a gear package of an attachmentpart according to the third embodiment of the invention.

DETAILED DESCRIPTION OF THE SHOWN EMBODIMENT OF THE INVENTION

In FIG. 1 an attachment part 10 according to a specific embodiment ofthe invention is shown.

The attachment part 10 comprises an elongate housing 11, 12 comprisingan upper housing part 11 and an interconnected lower housing part 12.

An input connector 13 for connection to an output shaft of a powerwrench is arranged at a first end of the housing 11, 12, and an outputconnector 14 for connection to a joint to be tightened is arranged at anopposite second end of the housing. The housing parts 11, 12 are heldtogether by means of a number of screws 15-21. In the shown embodiment,the housing parts 11 and 12 are held together by screws 15-21 only. Theuse of screws only minimises the risk of creating unwanted tensions inthe housing, which may otherwise appear when screws are combined withother attachment devices such as rigid connection pins. Namely, there isa play between the screw holes and the screws in one of the housingparts.

In the shown embodiment the screw holes of the lower housing part 12include a gap, while the screw holes of the upper housing part 11 arethreaded so as to form a joint with the screws 15-21. The gaps make itpossible for the housing parts 11 and 12 to move slightly with respectto each other. In FIG. 1 it is visible that the screws 15-21 are screwedinto threaded holes through the upper housing part 11, such that the endpart of at least some of them (15-17) are visible in FIG. 1, from theupper side of the attachment part 10. The screw heads of the attachmentpart are accessed from the lower side (not shown) of the attachment part10.

An attachment part for e.g. a power wrench is used in confined spaceswhere it may not be possible to use an ordinary power wrench, due tothat it is difficult or impossible to access the bolt or nut to bescrewed. Hence, the size of the attachment part is an important feature.The attachment part 10 according to the invention has a constructionthat allows it to be thinner than a conventional attachment part of thesame accuracy and torque capacity. This will be apparent from thedescription below.

In FIG. 2, the attachment part 10 is shown with the upper housing part11 removed, such that the interior of the attachment part 10 is visible.From FIG. 2 it is apparent that the input connector 13 is rigidlyconnected to an input gear wheel 22, and that the output connector 14 isrigidly connected to an output gear wheel 23. In fact, in the shownspecific embodiment, the input connector 13 is integral with the inputgear wheel 22, and that the output connector 14 is integral with theoutput gear wheel 23, such that both gear wheels 22 and 23 are formed asindividual integral pieces with teeth on the outside and a connector onthe inside.

The input connector 13 of the embodiment shown in FIGS. 1-3 includes asquare interface to connect to an output end of a power wrench. In theattachment part 10′ shown in FIGS. 7 and 8, the input gearing includesan angular gear wheel, such that the respective axes of the input shaft54 and the gear wheels lie in different planes. The axe of the inputshaft 54 is in the shown embodiment inclined 90° with respect to thegear wheels, but the angle of inclination may be adapted to any specificimplementation of the attachment part. The construction of the inputgearing is not relevant for this invention and is further well known toa person skilled in the art. Therefore, it will not be described indetail in this application. The invention covers both straight andinclined attachment parts. Further, the invention covers both attachmentparts 10′ with an open ended output 55 as the one shown in FIGS. 7-8,and attachment parts 10 with a closed output connector 14 as shown inFIGS. 1-3. The inventive construction is however specificallyadvantageous for attachment parts 10, both straight and inclined, with aclosed output connector 14.

As is apparent in FIG. 2, the input gear wheel 22 is drivingly connectedto the output gear wheel 23 via three intermediate gear wheels 24, 25,26. Each gear wheel has outer slanted teeth that connect the input gearwheel 22 to the output gear wheel 23. Slanted teeth are advantageousbecause they increase the contact surfaces between the gear wheels22-26, such that both the accuracy and the torque level of theattachment part 10 may be increased. However, the slanted teeth giverise to axial forces that will act on the gear wheels. This implies thatthe gear wheels need to be journalled in bearings that support them bothaxially and radially. Normally, axial supports build on the width of theattachment part. In the inventive arrangement, the gear wheels arehowever journalled in a manner that keeps the height of the attachmentpart 10 to a minimum.

The intermediate gear wheels, see specifically gear wheel 26, comprisean upper race 27 in which balls 28 are arranged. All intermediate gearwheels 24, 25, 26 comprise an upper race, but all races are not visiblein FIG. 2 as they are covered by upper axial supports 29 and 30. As isapparent in FIG. 1, these upper axial supports 30 and 31 are clampedinto through holes 48 that run through the upper housing part 11. Theupper axial supports 29-31 are arranged to support the balls 28 that arearranged inside said upper race(s) 27.

As is visible in FIG. 3 an upper part of each intermediate gear wheel24, 25, 26 is supported with respect to the housing 11, 12 by means of acorresponding upper axial support 29, 30, 31. Likewise, similar loweraxial supports 32, 33, 34 are clamped into through holes 48 that arearranged through the lower housing part 12. Also, a similar axialsupport 49 is arranged to support the lower part of the input gear wheel22. Other than that, the input gear wheel 22 is journalled in aconventional manner, e.g. by means of inter alia a radial bearing 50.For this first end of the attachment part 10, which is to be attached tothe power wrench, the size is not crucial.

One of the intermediate gear wheels 25 is shown in detail in FIG. 4. Asis visible in FIG. 3, this intermediate gear wheel 25 is arranged inbetween the two other intermediate gear wheels 24, 26. The intermediategear wheel 25 is arranged with a close fit inside the housing. There ishowever a small gap between the axial faces of the intermediate gearwheels 25 and the housing walls 11, 12. This gap is useful to avoidfrictional contact with the inside of the housing parts 11 and 12.

The intermediate gear wheels 24, 25, 26 are elastically journalled, suchthat there is an allowance, inside which the intermediate gear wheels24, 25, 26 are allowed to be positioned. In the shown embodiment, theelasticity is inherent in the axial supports 29-34.

In FIG. 5, a lower axial support 33 is shown in detail. The lower axialsupport 33 includes a cylindrical body 35, which is clamped into athrough hole 48 in the lower housing 12. Further, the lower axialsupport 33 includes an abutment portion 36 which is circular in theshown embodiment and adapted to be arranged in contact with the lowerhousing 12. The abutment portion 36 is separated from the cylindricalbody 35 by a circular recess 51. The circular recess 51 is a result ofthe machining of the axial support and allows for a close fit betweenthe abutment portion 36 and the inside wall of the housing. Radiallyoutside of the abutment portion 36 a circular flange 37 is arranged. Thecircular flange 37 has a partly hollow portion 53 which functions as arace and is arranged to support the bearing balls 38. Further, thecircular flange 37 is separated from the cylindrical body 35 by a flexportion 39 that allows the flange 37 to flex with respect to thecylindrical body 35 of the axial support 33, and hence with respect tothe housing 11, 12.

An advantage of the bearing arrangement of the shown embodiment is thatits construction has a high torsional strength. This is apparent fromFIG. 4. To a skilled person, the bearing arrangement of FIG. 4 has anO-configuration as opposed to an X-configuration, such as the bearingarrangement shown in FIG. 6, around the output gear wheel 23.

The O-configuration around the intermediate gear wheel 25 in FIG. 4 isadvantageous in that it is well adapted to receive the torsional effortsthat may appear during operation. If, for example, the torsional forcesinduced by the interaction between the slanted gears acts on theintermediate gear wheel 25 so as to rotate it clockwise as it appears inFIG. 4, the upper left ball 28 will be pressed upwards and slightly tothe right by the upper race 27 of the intermediate gear wheel 25. Thisforce will be positively received by the hollow portion 53 of the upperaxial support 30, which in turn is supported by the upper housing part11. Similarly, the lower right ball 38 will be pressed downwards andslightly to the left by the lower race 52, which force will bepositively received by the lower axial support 33, which in turn issupported by the lower housing part 12. The upper left bearing 28 andthe lower left bearing will 38 experience only limited forces in thisstate. Of course, as the intermediate gear wheel 25 and the balls arerotating, it is not a specific ball that is put under pressure, it isthe current location of each ball that is decisive for how much pressureis exerted on it, such that theoretically each ball experiences the sameforces when located at one specific location.

When the attachment part is driven in the opposite direction, so as toloosen instead of tightening a bolt or vice versa, the intermediate gearwheel 25 will be rotated in the opposite direction and the forces willact in the opposite direction on the intermediate gear wheel 25 so as toact to rotate it counter clockwise as it appears in FIG. 4. Hence, inthis state, the upper balls 28 will experience the highest forces at theposition that corresponds to the upper right position in the figure, andthe lower balls 38 will experience the highest forces at the positionthat corresponds to the lower left position in the figure.

Due to the inherent elasticity of the circular flanges 37 theintermediate gear wheels 24, 25, 26 will be allowed to be re-positionedto a certain degree with respect to the housing 11, 12. This will reducethe stress between the housing parts 11, 12 and the intermediate gearwheels 24, 25, 26, and thereby minimise the risk of ruptures due tofatigue.

In different applications it is preferable to use a various number ofintermediate gear wheels. There has to be at least one intermediate gearwheel, and normally there are two or three intermediate gear wheelslocated between the input gear wheel and the output gear wheel. Ofcourse, there may be even more intermediate gear wheels for certainapplications.

FIG. 6 shows a cross section of the second end of the attachment part10. The second end involves an output connector 14 for connection to ajoint to be tightened. In the shown embodiment the output connector 14consists of a hexagonal socket, which is integral with the output gearwheel 23. The output gear wheel 23 is journalled with respect to thehousing 11, 12 by means of balls 40, 41 that are arranged between outerraces 42, 43 on the output gear wheel 23 and corresponding races 44, 45on the inside of the housing 11, 12. Specifically, a first set of balls40 are arranged in an upper outer race 42 on the upper periphery of theoutput gear wheel 23, and a second set of balls 41 are arranged in alower outer race 43 on the lower periphery of the output gear wheel 23.Both the upper housing 11 and the lower housing 12 has a circularopening 46, 47, respectively, through which end parts 49 of the outputgear wheel 23 extend. The housings 11 and 12 comprise races 44, 45 thatcover the balls 40, 41. The races 44, 45 are formed as circular recessesin the portion of the housing 11, 12 adjacent the circular openings 46,47. The end parts 49 of the output gear wheel 23 are arranged with aclose fit inside these circular openings 46, 47 of the housing 11, 12.

In FIGS. 9-12 a third embodiment of an attachment part 10″ according tothe invention is shown. This third embodiment resembles the attachmentpart according to the first and second embodiment in that it comprisesan upper and a lower housing part 11 and 12, respectively. The housingparts 11,12 are attached to each other by means of screws 15-21. This isshown in FIGS. 9-10. Further, attachment pieces 57-59 are arrangedthrough a centre line of the attachment part 10″. The attachment pieces57-59 are arranged to clamp axial supports 29′,30′,31′ of the upperhousing part 11 to axial supports 32′,33′,34′ of the lower housing part12.

As is apparent in FIGS. 11 and 12 the balls 28 in the upper race 27 ofthe intermediate gear wheels 24-26 are fully supported by an upper axialsupport 29′,30′,31′. The balls 28 in the lower race 53 are fullysupported by a lower axial support 32′,33′,34′. The lower and upperaxial supports 29′-34′ are connected to each other via an attachmentpiece 57-59 that runs through the centre of the intermediate gear wheel24,25,26, such that an upper axial support 29′-31′, a set of upper balls28, a gear wheel 24,25,26, a set of lower balls 38, and a lower axialsupport 32′,33′,34′ forms a releasable gear package. This isadvantageous in that part of the axial forces will be taken up in thegear package, i.e. by the attachment piece 57-59, such that the effortson the housing 11 and 12 will be less important.

In the shown embodiment the attachment pieces 57-59 are screws and theupper axial supports 29′,30′,31′ have a threaded portion 63 inside whichthe tip of the attachment pieces 57-59 is to be screwed. See FIG. 12.

From FIG. 12 it is also apparent that the upper and lower axial supports30′,33′ include a body portion 35 that is arranged to be received inthrough holes in the upper and lower housing part 11,12, respectively.The lower axial support 33′ comprises a protrusion 61 that is arrangedto fit tightly inside a recessed portion 62 of the upper axial support30′. The protrusion 61 is arranged along the centre of the lower axialsupport 33′ adjacent the through hole for the attachment piece 58. Theinteraction between the protrusion 61 of the lower axial support 33′ andthe recessed portion 62 of the upper axial support 30′ will, incombination with the clamp force of the attachment piece 58, make surethat the upper and lower axial supports 30′,33′ are fixed with respectto each other. One or more shin(s) 60 may be arranged between the upperand lower axial supports 30′,33′ in order to achieve a correct distancebetween the supports 30′,33′. It is however also possible to produce theaxial supports with such a precision that no shins will be needed.

The upper and lower axial supports 30′,33′ include a support ring 64arranged to support the balls 28,38 at one end and to abut the housing11,12 at the other end.

Above, the invention has been described with reference to two specificembodiments. The invention is however not limited to either of theseembodiments. It is obvious to a person skilled in the art that theinvention may be modified within its scope, which is defined by thefollowing claims.

1-12. (canceled)
 13. An attachment part for tightening joints,comprising: an elongate housing including an upper housing part and aninterconnected lower housing part, an input gear wheel for connection toan output shaft of a power wrench, the input gear wheel arranged at afirst end of the housing, an output gear wheel for connection to a jointto be tightened, the output gear wheel arranged at a second end of thehousing, and at least one intermediate gear wheel, which is arrangedinside the housing to transmit rotation of the input gear wheel to theoutput gear wheel, wherein each gear wheel has outer slanted teeth thatconnect the gear wheels and transmit rotation there between, wherein theat least one intermediate gear wheel comprises: an upper race, which isarranged inside the at least one intermediate gear wheel and faces theupper housing part, wherein balls are arranged in said upper race atleast partly inside the at least one intermediate gear wheel to supportan upper part thereof with respect to the housing, and a lower race,which is arranged inside the at least one intermediate gear wheel andfaces the lower housing part, wherein balls are arranged in said lowerrace at least partly inside the at least one intermediate gear wheel tosupport a lower part thereof with respect to the housing, wherein theballs in the upper and lower races are fully supported by upper andlower axial supports, respectively, the axial supports being connectedto each other via an attachment piece that runs through a centre of theintermediate gear wheel, such that the upper and lower axial supports,balls and a gear wheel form a releasable gear package.
 14. Theattachment part according to claim 13, wherein the upper and lower racesare arranged at a position inside the at least one intermediate gearwheel that allows the entirety of the balls to fit inside the at leastone intermediate gear wheel.
 15. The attachment part according to claim13, wherein the attachment piece comprises a screw and wherein one ofthe axial supports has a threaded opening inside which a tip of thescrew is to be screwed.
 16. The attachment part according to claim 13,wherein the upper and lower axial supports include a body portion thatis arranged to be received in through holes in the upper and lowerhousing parts, respectively.
 17. The attachment part according to claim13, wherein the output gear wheel is journalled inside the housing, bymeans of balls that are arranged between an upper and lower outerperiphery of the output gear wheel and the respective housing part. 18.The attachment part according to claim 13, wherein the attachment partincludes at least two intermediate gear wheels.
 19. The attachment partaccording to claim 18, wherein the attachment part includes threeintermediate gear wheels.
 20. The attachment part according to claim 13,wherein the upper and lower housing parts are held together by screwsoutside the intermediate gear wheel, and wherein there is a gap betweenthe screws and one of the housing parts, such that there is an allowanceinside which the upper and lower housing parts may slide with respect toeach other.